The present invention relates to a thin battery with a laminate casing, wherein the electricity generating elements are packaged in a casing which is formed by superposing two sheets of laminate and joining the periphery thereof.
Thin, lightweight non-aqueous electrolytic batteries with flexible laminate casing such as lithium polymer rechargeable battery are most suitable for use as the drive power sources of thin, portable electronic devices, and particularly of portable telephones that have become so popular in recent years.
FIG. 35 is a plan view showing a lithium polymer rechargeable battery as one example of a prior art battery with a laminate casing. FIG. 36 is a cross-sectional view seen along the line XXXVIxe2x80x94XXXVI of FIG. 35. As shown in FIG. 36, a plurality of electrode plate modules 3 are stacked up to form a stacked electrode assembly 2, which is accommodated in a casing 1 made of a laminate sheet. Because of such flatness, the stacked electrode assembly 2, being enveloped in a laminate sheet casing 1, is advantageously used for constructing a flat and lightweight battery.
Referring to FIG. 37, the electrode plate module 3 includes a negative electrode plate 4 composed of a negative electrode current collector 7 and negative electrode mixture layers 8 formed on both sides thereof, a pair of positive electrode plates 9 composed of a positive electrode current collector 10 and positive electrode mixture layers 11 formed on both sides thereof. The positive electrode plates 9 are superposed on both sides of the negative electrode plates 4 with intervening separators 12 therebetween to form an integral unit of electrode plates. These electrode plate modules 3 are stacked upon one another to form the electrode assembly 2 shown in FIG. 36 and to attain a required voltage or battery capacity. Negative electrode terminals 7a extend from one end of each of the negative electrode current collectors 7, and these negative electrode terminals 7a are bundled and welded together, with a negative electrode lead 13 welded to the weld joint. Similarly, positive electrode terminals 10a shown in FIG. 37 which extend from one end of each of the positive electrode current collectors 10 are bundled together, and a positive electrode lead 14 shown in FIG. 35 is welded to the weld joints of the positive electrode terminals.
The casing 1 consists of a laminate sheet, including a metal layer such as an aluminum foil for providing air-tight and liquid-tight properties, with a resin layer having a high melting point bonded to an outer side of the metal layer, and another resin layer of metamorphic polypropylene bonded to an inner side of the metal layer. The laminate sheet is folded in two as shown in FIG. 38, and formed into an envelope shape by heat-sealing the opposite edges P1, P2. The stacked electrode assembly 2 is inserted into the casing 1 through the open end, liquid electrolyte is injected thereinto, and the open end edge P3 is heat-sealed such that the positive electrode lead 14 and the negative electrode lead 13 extend to the outside as shown in FIG. 35.
Japanese Laid-open Patent Application No. 11-288698 proposes bonding of an additional resin seat or a sealing material 17, by applying heat, to both sides of the positive electrode lead 14 and the negative electrode lead 13 where they pass through the open end edge P3, so that the portions of the open end edge P3 where the positive electrode lead 14 and the negative electrode lead 13 pass through are reinforced with the additional resin sheet 17 to have enhanced leakage-proof property. For the resin sheet 17, a copolymer of ionomer, ethylene and acrylic acid, polyethylene resin, polypropylene resin, polyamide resin, polyester resin or polyurethane resin are used.
Another conventional battery employs a casing 18 having a construction shown in FIG. 39. The casing 18 made of a laminate sheet similar to the one mentioned above includes a base part 18a, which is one side of the folded laminate sheet, the other side thereof forming a cover 18b. The base part 18a has a recess 18b for accommodating the stacked electrode assembly 2 therein. One advantage of this casing 18 is that, as compared to the envelop-shaped casing 1, the electrode assembly 2 can readily be inserted into the recess 18b of the base part 18a, with the cover 18c being widely opened.
The casing 18 has seal flanges 18d, 18e, and 18f, and when the stacked electrode assembly 2 is accommodated within the recess 18b, the positive electrode lead 14 and the negative electrode lead 13 sit on the seal flange 18e and extend to the outside of the base part 18a. The cover 18c is then closed, with its two opposite sides being heat-sealed with the seal flanges 18d, 18f, and liquid electrolyte is injected into the casing through the openings between the remaining seal flange 18e and one end edge of the cover 18c. Thereafter, the seal flange 18e and the end edge of the cover 18c is welded to seal the casing 18.
Similarly to the envelop type casing 1, a resin sheet 17 made of polypropylene film is joined to the positive electrode lead 14 and the negative electrode lead 13 from both sides where they pass through the seal flange 18e end, so that the sealing property at this end will not be deteriorated and reliable leakage-proof property is ensured. One side of the recess 18b, at which the positive electrode lead 14 and the negative electrode lead 13 extend to the outside, has an inclined surface 18g, so as to accommodate the negative electrode terminals 7a and positive electrode terminals 10a, which take a triangular shape as they are bundled together at a location near the seal flange 18e. 
In neither of the above-described batteries using either the casing 1 or 18, the stacked electrode assembly 2 inside is not sufficiently retained in position, because it is accommodated within the casing made of a flexible laminate sheet with a certain gap provided in the direction parallel with the direction of the two extending leads 13, 14. As a result, continuous vibration transmitted from the portable electronic equipment in which the battery is installed may cause the stacked electrode assembly 2 to displace within the casing 1 or 18, resulting in offsetting of the stacked electrode plate modules 3.
Displacement of the stacked electrode assembly 2 or offsetting of the stacked electrode plates 3 give rise to various problems. For example, the joints between the negative and positive electrode leads 13, 14 and their respective terminals 7a, 10a, and the joints between the leads and the casing 1, 18, which are mechanically weak, may be subjected to repeated bending, resulting in deformation or disconnection in these portions. The casing 1, 18 is also constantly subjected to the risk of being damaged by pointed edges or burrs on the electrode assembly 2. Also, the intermediate metal layer of the laminate sheet casing 1, 18 may contact the electrode assembly 2, whereby a local cell is formed due to the intervening electrolyte, resulting in development of gas, or short-circuiting across electrodes 9, 4 or terminals 7a, 10a of opposite polarity. These troubles may lead to malfunctioning of battery output, electrolyte leakage, or corrosion of the metal layer in the laminate sheet casing caused by the electrolyte.
All of these troubles result from the structure wherein the electrode assembly 2 is not retained in position within the casing 1, 18. The electrode assembly 2, in its widthwise direction which is orthogonal to the direction along the leads 13, 14, snugly fits in the casing 1, 18, because there are no leads in this direction. However, when welding the resin sheet 17 to the casing 1, 18 with an automatic welder, welding points are spaced from the negative and positive electrode terminals 7a, 10a, in order to achieve reliable welding by positively preventing occurrence of bad welds caused by contact of the welding member with the negative electrode terminals 7a or positive electrode terminals 10a. Thus a gap inevitably exists between the electrode assembly 2 and the casing 1, 18 in the direction along the leads 13, 14.
Portable phones, in particular, in which such battery with laminate casing is used commonly, are carried about in the pockets of clothing or in brief cases, so that batteries are frequently subjected to vibration and even considerable impacts upon the device being dropped. Portable telephones thus have a disadvantage that battery breakage or electrolyte leakage occurs frequently.
One of the conventional countermeasures to prevent these troubles is to provide a band stretching over both ends of the electrode plate group 2 in order to prevent the offsetting of the positive and negative electrode plates 9, 4 upon being subjected to vibration or impact. However, such band merely restrains the electrode plates and cannot prevent deformation of the leads 13, 14 or their weld joints which may be caused by the impact. Thus there remains the risk of internal short-circuiting across the terminals 10a, 7a of opposite polarity.
It has also been proposed to fix the plurality of terminals 10a, 7a of the same polarity in mutually spaced relationship with a conductive adhesive, when constructing the electrode assembly 2. This gives allowance for slight offsetting or displacement of the terminals 10a, 7a of opposite polarity with respect to each other during the assembling step of the electrode assembly 2. Nevertheless, it is not sufficient to prevent offsetting or displacement of the electrode plate modules 3 within the casing 1, 18 caused by vibration or impact, and there remains the risk of internal short-circuiting across the terminals 10a, 7a of opposite polarity caused by crushed or deformed leads 13, 14 or their weld joints.
The present invention is directed to solve the problems pointed out above, and therefore, an object of the invention is to provide a battery with laminate casing which can withstand repeated vibration or large impact, whereby the possibility of occurrence of output failure, electrolyte leakage, or corrosion of the casing is remarkably reduced.
To achieve the object, the present invention provides a battery including:
liquid electrolyte and an electrode assembly, both accommodated within a sealed casing made of a laminate sheet, the electrode assembly including a plurality of positive electrode plates and a plurality of negative electrode plates stacked upon one another with a plurality of intervening separators therebetween, the positive electrode plates having respective positive electrode terminals and a positive electrode lead joined to the positive electrode terminals, and the negative electrode plates having respective negative electrode terminals and a negative electrode lead joined to the negative electrode terminals, these positive electrode lead and negative electrode lead being extended to the outside through one end of the casing; and
a means for fixing the electrode assembly in position within the casing.
According to this battery, the electrode assembly inside the battery is fixed in position even if the portable electronic device in which the battery is mounted is subjected to frequent or repeated vibration or large shock. Therefore, there is no risk in this battery that the positive and negative electrode leads joined to their respective electrode plates are bent or cut, or that the flexible laminate casing is damaged by pointed corners or burrs on the electrode assembly. Accordingly, various troubles, such as short-circuiting across the intermediate metal layer of the casing and the electrode assembly, battery output failure, leakage of electrolyte, and corrosion of the metal layer in the casing by the electrolyte, are all prevented.
The electrode assembly fixing means may be constructed of a frame surrounding the periphery of the electrode assembly and accommodated within the casing with the electrode assembly. According to one aspect of the invention, the frame includes
a rectangular frame portion surrounding the periphery of the electrode assembly,
a pair of protective pieces projecting outwards from opposite side edges of one end of the frame portion to cover joints between the positive and negative electrode terminals and the positive and negative electrode leads from both sides, the frame portion having through holes along one side thereof for allowing the positive and negative electrode terminals to extend to the outside.
Thereby, the joints between the positive and negative electrode terminals and their leads, which are mechanically weak, are protected against impacts as they are arranged within the space enclosed by the pair of protective pieces, and are prevented from being deformed or disconnected. Also, when sealing the casing in the assembling step, there is no risk that the welding tool of an automatic welder may contact the positive or negative electrode terminals. Therefore, the casing can be sealed at a nearest possible position to the distal ends of the pair of protective pieces. As a result, the frame is enclosed in the casing without any free space therein, and the electrode assembly surrounded by the frame is reliably fixed within the casing even in a condition with repeated vibration or large shocks.
According to another aspect of the invention, the frame includes a first part consisting of a first half frame and a second part consisting of a second half frame for holding the periphery of the electrode assembly from both sides, the first half frame and the second half frame being integral with each other via a bendable hinge and superposed upon one another, and respectively having a protective piece extending outwards from one end thereof opposite from the hinge, and one of the first half frame and the second half frame having notches therein for passing through the positive and negative electrode terminals to the outside.
The frame is one piece but can simply be attached to the electrode assembly such as to surround the periphery thereof by bending the frame into two by means of the hinge. The cut-outs provided to one of the half frames form through holes when closed by the side edge of other half frame, so as to allow the positive and negative electrode terminals to extend to the outside while fixed in position.
Preferably, the first and the second half frames have engagement pieces for making locking engagement with each other on one end thereof opposite from the hinge, so as to securely attach the frame to the electrode assembly.
Preferably, the protective pieces of the first and the second half frames come to face each other with a space formed therebetween and are connected via a connector when the first and the second half frames are superposed upon one another via the hinge. Thereby the rigidity of the protective pieces is enhanced and the space formed therein is hardly deformable. Thus the joints between the electrode terminals and their leads are reliably protected from shocks and the electrode assembly is even more securely held in position.
According to yet another aspect of the invention, the frame includes a first part consisting of a first half frame and a second part consisting of a second half frame for holding the periphery of the electrode assembly from both sides, the first half frame and the second half frame being separate from each other and respectively having a protective piece extending outwards from one end thereof, and engagement pieces along more than one side thereof for making locking engagement with each other to couple the first and the second parts when superposed, and one of the first half frame and the second half frame having notches therein for passing through the positive and negative electrode terminals to the outside. In addition to the electrode assembly protection effect and position displacement prevention effect, this construction enables easier fabrication of the frame.
According to a further aspect of the invention, the electrode assembly fixing means is a frame surrounding the periphery of the electrode assembly and accommodated within the casing with the electrode assembly. The frame includes
an abutment portion making contact with one end face of the electrode assembly from which the positive and negative electrode terminals extend, the abutment portion being formed with through holes for passing through the positive and negative electrode terminals,
a pair of legs extending from both ends of the abutment portion to cover both side faces of the electrode assembly, and
a pair of protective pieces extending from opposite side edges of the abutment portion in a direction opposite from the pair of legs so as to cover joints between the positive and negative electrode terminals and their respective leads from both sides.
Thereby, the joints between the positive and negative electrode terminals and their leads, which are mechanically weak, are protected against impacts as they are arranged within the space enclosed by the pair of protective pieces, and are prevented from being deformed or disconnected. The frame covers at least one end face and both side faces of the rectangular electrode assembly within the casing, protects the casing from being damaged by pointed corners or burrs on the electrode assembly, and prevents short-circuiting across the electrode assembly and the metal layer in the casing made of laminate sheet. Further, the frame can be attached to the electrode assembly by simply spreading the pair of legs, causing the abutment portion to warp, and inserting the electrode assembly between the pair of legs of the frame, with the electrode terminals being passed through the through holes. The frame has a more simplified construction covering only three sides of the electrode assembly, resulting in a decrease in material cost.
Preferably, the pair of protective pieces have a length extending to a portion near a joint between the positive and the negative electrode leads and the casing. Thereby, the casing can be sealed at a nearest possible position to the distal ends of the pair of protective pieces. As a result, the frame is enclosed in the casing without any free space therein, and the electrode assembly surrounded by the frame is reliably fixed within the casing even in a condition with repeated vibration or large shocks.
Preferably, the pair of protective pieces have resiliency so as to bend inwards when pressed by the laminate sheet forming the casing which is superposed and joined together at its periphery. Thereby, when the sheets of flexible laminate of the casing are superposed and joined, the pair of protective pieces are pressed to deform toward each other, forming a space therein which conforms to the shape of the bundles of electrode terminals having a substantially triangular cross-section. Thus the rigidity of the protective pieces is enhanced, ensuring that joints between the electrode terminals and leads are reliably prevented from damage or deformation.
Alternatively, the frame may include a cover integral with the frame extending from opposite side edges of the abutment portion in a direction opposite from the pair of legs so as to form a space therein having a triangular cross-section so as to accommodate the joints between the positive and negative electrode terminals and their respective leads within the space, the cover including through holes for passing through the positive and negative electrode terminals. The cover integral with the frame forms a space therein which has a triangular cross-section and is higher in rigidity than a pair of protective pieces. Thus it is ensured that the joints between the electrode terminals and leads are reliably protected from vibration or shocks and prevented from damage and deformation. Since the cover has an inclined surface on its inner side, it also offers the advantage that, during the assembly of the battery, the electrode terminals can be smoothly guided into the through holes along this inclined surface.
Preferably, the pair of legs has a U-shaped cross-section so as to fit onto the side edges of the electrode assembly, so as to reliably prevent offsetting of the plurality of stacked electrode plate modules of the electrode assembly even if subjected to large shocks or repeated vibration.
Alternatively, the frame may further include a pair of support frames integrally formed with the pair of legs, the support frames extending respectively from the distal ends of the legs inwards so as to cover the two corners of the electrode assembly at the end opposite from the end where the positive and negative electrode terminals extend. With this construction, while the frame can readily be attached to the electrode assembly, the two corners on one end of the electrode assembly opposite from the electrode terminals are securely accommodated within the support frames, i.e., while the construction is simplified, the frame substantially surrounds the periphery of the electrode assembly. Thus the offsetting of the plurality of stacked electrode plate modules of the electrode assembly is reliably prevented.
Alternatively, the frame may include a pair of connector plates for closing the distal ends of the pair of legs so as to cover the two corners of the electrode assembly at the end opposite from the end where the positive and negative electrode terminals extend. The construction of this frame and attachment thereof to the electrode assembly are further simplified as compared to the one described above with the pair of support frames, yet it offers the same advantages as mentioned above.
According to another aspect of the invention, the electrode assembly fixing means is an insulating spacer abutted on one end face of the rectangular electrode assembly where the positive and negative electrode terminals extend, and an adhesive tape for fixing the insulating spacer to the electrode assembly, the insulating spacer including a bottom abutting on one end face of the electrode assembly except for the positive and negative electrode terminals, a pair of side walls standing upright from both side edges of the bottom to a height for covering joints between the positive and negative electrode terminals and the positive and negative electrode leads, the bottom and the side walls being formed in one piece, and the adhesive tape being stuck over to the electrode assembly and the insulating spacer so as to cover four corners at one end of the electrode assembly.
This fixing means is composed of an insulating spacer which is further simplified as compared to the various frames described above, and therefore is lower in material cost. The insulating spacer, with its bottom abutted on one end face of the electrode assembly, is fixed to the electrode assembly with the adhesive tape, whereby the plurality of stacked electrode plate modules of the electrode assembly are restricted from offsetting even if the battery is subjected to vibration or shocks. The pair of side walls cover the mechanically weak joints between the electrode terminals and leads from both sides and protect same from shocks. Also, the side walls fill up the space between the casing and one end face of the electrode assembly where the electrode terminals extend, whereby, while it is simply constructed, it effectively restricts free movement of the electrode assembly when the battery is subjected to vibration or shocks. Furthermore, the insulating spacer is particularly effective for preventing the electrode terminals or pointed corners of the electrode assembly from contacting the inner resin layer of the flexible laminate casing, and it ensures prevention of damages to the casing.
Alternatively, an additional adhesive tape may be stuck to the opposite end of the electrode assembly so as to cover the four corners thereof. By covering all corners of the electrode assembly with adhesive tape, the flexible laminate casing is prevented from being damaged by pointed corners of the electrode assembly, even if it moves because of vibration or shocks.
In one aspect of the invention, the electrode assembly includes a plurality of stacked electrode plate modules, each of the electrode plate modules including a negative electrode plate, a pair of positive electrode plates superposed on both sides of the negative electrode plate with intervening separators therebetween, and positive electrode terminals respectively extending from the pair of positive electrode plates. In this construction, it is preferable that the positive electrode terminals be provided with an insulative coating at least on one side thereof facing an adjacent electrode plate module. Thereby, even if the negative electrode plates are formed larger than the positive electrode plates because of dimensional errors, and even if the electrode plates are offset from each other because of vibration or shocks, the insulative coating will prevent short-circuiting across both electrode plates.
According to yet another aspect of the present invention, the electrode assembly fixing means is an insulating spacer abutted on one end face of the rectangular electrode assembly where the positive and negative electrode terminals extend, and strips of adhesive tapes for fixing the insulating spacer to the electrode assembly, the insulating spacer including a bottom abutting on one end face of the electrode assembly except for the positive and negative electrode terminals, a pair of side walls standing upright from both side edges of the bottom to a height for covering joints between the positive and negative electrode terminals and the positive and negative electrode leads, the bottom and the side walls being formed in one piece, and the strips of adhesive tapes having a length for covering opposite side edges of the electrode assembly along the length thereof.
With this construction, the battery is low in material cost because of the more simplified insulating spacer, while it ensures that each of the stacked electrode plate modules is restricted from displacing, and the electrode assembly itself is fixed in position even when the battery receives vibration or shocks, thereby protecting the joints between the electrode terminals and leads from shocks. In addition, since all corners of the electrode assembly are covered by the adhesive tapes, the inner resin layer of the flexible laminate casing is prevented from being damaged by pointed corners or edges of the electrode assembly, even if it moves because of vibration or shocks.
In cases where a pair of adhesive tapes are employed as described above, it is preferable to trim one end face and both side end faces of the electrode assembly to have flat surfaces. This is particularly so when the laminate sheet casing has the configuration wherein it has a recess in which the electrode assembly is fixedly fitted, because in such case it is desirable to cover the sharpened edges of the electrode assembly to protect the inner resin layer of the laminate sheet casing.
According to a further aspect of the present invention, the electrode assembly fixing means is an insulating spacer made of a material resistant to the electrolyte and having a higher melting point than that of the casing, and accommodated within the casing together with the electrode assembly, the insulating spacer having a shape corresponding to a space defined by one end face of the electrode assembly where the positive and negative electrode terminals extend, and an inner surface of the casing opposite the end face of the electrode assembly, and including a pair of through holes for passing through the positive and negative electrode leads respectively joined to the positive and negative electrode terminals to the outside, and a reinforcing portion provided between the through holes such as to make tight contact with the one end face of the electrode assembly.
With this construction, before inserting the electrode assembly into the casing, the positive and negative electrode leads are passed through the pair of through holes in the insulating spacer, and the spacer is attached to one end of the electrode assembly. After inserting the electrode assembly into the casing, the casing is sealed by applying heat and pressure. Here, since the insulating spacer has a higher melting point than the casing, the laminate sheet casing can be sealed at a nearest possible position to the insulating spacer. The insulating spacer is packed within the casing with it s reinforcing portion tightly contacted to one end of the electrode assembly, filling the space between the electrode assembly and the casing. Thus the electrode assembly is securely held in position within the casing. Also, this insulating spacer is a simply constructed one-piece product, whereby a reduction in material cost and the number of assembling steps is achieved.
For such insulating spacer, a flat plate member may be used which is bent along at least two grooves into the shape corresponding to the space defined by one end face of the electrode assembly and the inner surface of the casing opposite the end face of the electrode assembly.
As compared to the one-piece spacer, the flat plate member can be fabricated at a lower cost and assembled simply by bending, while offering the same advantages as those of the one-piece product.
Preferably, the insulating spacer and the casing are joined together by applying heat and pressure. By joining the casing with the insulating spacer which has high rigidity and is fixed to the electrode assembly, the electrode assembly is fixed within the casing even more reliably.
Preferably, the positive and negative electrode leads are respectively provided with folded-back portions inside the insulating spacer near a point where the positive and negative electrode terminals are joined thereto. Thereby, even if the positive or negative electrode leads are subjected to tension from the outside, such can be absorbed by folded-back portions that serve as a spring. Thus, as compared to prior art battery of this type, the electrode leads of the battery of the invention can withstand a much larger external force.
According to yet another aspect of the invention, the electrode assembly fixing means is made of a pair of flat plate spacers made of a material resistant to the electrolyte and having resiliency, and accommodated within the casing together with the electrode assembly, the flat plate spacers being joined together such as to cover joints between the positive and negative electrode terminals of the electrode assembly as being deformed to conform to the contour of the joints, one end face of each of the flat plate spacers making contact with one end face of the electrode assembly where the positive and negative electrode terminals extend.
The pair of flat plate spacers joined together, when encased within the casing with the electrode assembly, do not allow any free movement of the electrode assembly. The flat plate spacers have resiliency and can deform to be joined together, covering the electrode terminals from both sides. Therefore, while it has a simple flat plate shape and is lower in material cost, it offers the same advantages as those of the above-described insulating spacer.
According to a further aspect of the invention, the electrode assembly fixing means is a metamorphic olefin resin provided at a plurality of locations between the casing and the electrode assembly accommodated therein, the casing and the electrode assembly being joined together through the metamorphic olefin resin by applying heat and pressure. This fixing means is simple and low-cost, and by directly adhering the electrode assembly to the casing, it prevents troubles such as battery output failure, electrolyte leakage, and corrosion of metal layer in the casing by the electrolyte. Also, even when the thickness or the shape of the electrode assembly is changed because of modification in the number or the size of the electrode plates, no special adjustment is needed for the fixing means in the assembling step.
According to a yet another aspect of the invention, the electrode assembly fixing means is a tape attached to the electrode assembly for maintaining the shape thereof, the casing and the electrode assembly being joined together through the tape by applying heat and pressure. This fixing means is simple and low-cost, as it utilizes existing fixing tape as an adhesive, and by directly adhering the electrode assembly to the casing via the tape, it prevents troubles such as battery output failure, electrolyte leakage, and corrosion of metal layer in the casing by the electrolyte. Also, even when the thickness or the shape of the electrode assembly is changed because of modification in the number or the size of the electrode plates, no special adjustment is needed for the fixing means in the assembling step.
According to a further aspect of the invention, the electrode assembly fixing means is composed of a pair of inclined surfaces formed in one side face of a recess formed in the casing for receiving the electrode assembly, and abutting surfaces provided between the inclined surfaces and on both outer sides thereof, for making tight contact with one end face of the electrode assembly accommodated in the recess, the positive and negative electrode terminals of the electrode assembly being respectively fitted onto the inclined surfaces.
Thereby, when the electrode assembly is inserted in the recess, the abutting surfaces make tight contact with one end face of the electrode assembly where the leads extend. Thus the electrode assembly is held in position within the recess, and troubles such as battery output failure, electrolyte leakage, and corrosion of metal layer in the casing are all prevented. Also, with this fixing means, the electrode assembly is fixed by just inserting same into the recess, and no fixing process step is required such as applying heat with a hot plate.
Alternatively, the separators may have larger outer dimensions than those of the positive electrode plates and the negative electrode plates, so that the separators project from both sides of the electrode assembly and prevent positive and negative electrode plates from contacting the laminate sheet casing.
In any aspects of the invention described above, the casing may be made of a laminate sheet bent in two and formed into a bag shape by joining the periphery thereof, or may be made of a laminate sheet bent in two, and having a base part forming a recess for receiving the electrode assembly and a cover for closing the recess.
It should be noted that all the effects and advantages of the present invention described above will also be achieved if the electrode assembly is constructed of positive and negative electrode plates wound into a coil with intervening separators therebetween and pressed into a flat shape, instead of the stacked electrode plates.